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114              PRACTICAL ORGANIC CHEMISTRY

neck. Ten c.c. of water are now added gradually from the tap-
funnel.    Hyclrioclic acid is evolved, and, after being freed from
iodine in the LJ-tllke> 'ls absorbed by the water. When the water
has been added, the liquid is gently heated over a small flame
until no more fumes issue from the delivery-tube.    The aqueous
solution of hydriodic acid is distilled with a thermometer, and
the portion boiling at 125° and above is collected separately.    It
consists [of strong hydriodic acid .solution,  containing  about
57  per cent,   of HI.    The   malic  acid  is   dissolved   in   the
hydriodic   acid    and   poured   into   a   stout-walled   tube   for
sealing.    The red phosphorus is added, and the tube sealed      \
in the usual way (see p. 24).    It is heated in the tube-furnace
for six hours at 120°.    On removing the tube it is found to be
filled with  crystals of succinic acid mixed with  iodine.   The     {*
contents are poured into a basin and evaporated to dryness on     >v
the water-bath.    The residue, when cold, is stirred with a little
chloroform to dissolve the free iodine, which is then decanted,     *
and the process repeated if necessary.    After warming to drive     {
off the chloroform, the substance is dissolved in hot water and     "
set aside to crystallise. Succinic acid crystallises in long prisms.
Yield 5 grams.
" COOH.CHOH.CHo.COOH + 2HI = COOH.CHo.CHo.COOH
+ H2O 4- I3.
Properties.—Colourless prisms ; m. p. 180°. On distillation,
the acid loses water and is converted into the anhydride.
Reaction.—r. Make a neutral solution by boiling with an
excess of ammonia, and add to one portion, calcium chloride ;
no precipitate is formed ; to another portion add a drop or
two of ferric chloride ; a brown precipitate of ferric succinate
is thrown down. See Appendix, p. 261.
CH(OH).COOH       :
Tartaric Acid (Dihydroxysuccinic Acid), |
CH(OH).COOH
Scheele (1769).                                      |
The acid potassium or calcium tartrates are found in many
plants ; but the chief source of tartaric acid is the impure acid
potassium salt, which separates out as wine-lees, or argol from
grape-juice in process of fermentation.                                        ^
Properties.—The   acid    crystallises   in   monoclinic   prisms,     <